The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This invention relates to a composition for treating a borehole such as an oil or gas well, comprising fibres and hot melt adhesives. Such compositions find uses in control of borehole instability and lost circulation problems.
In the oilfield industry, various products and techniques have been used in the past to reduce lost circulation and wellbore consolidation issues, which occur in many parts of the world and cause undesirable losses of time and money. Known methods of curing lost circulation are the use of loss circulation materials (LCMs) in drilling fluid and/or in cement or polymer systems, and the use of single-type or mixed fibres. However, the success rate and efficiency are often not satisfactory.
The present invention involves the use of hot melt adhesives. Hot melt adhesives are not widely used in the oilfield industry. The invention is based on the recognition that the ability of hot melt adhesives to dissolve completely or partially depending on adhesive formulation and temperature range makes them suitable for oilfield applications.
Hot melt adhesives are solvent-free adhesives which are solid up to a certain temperature, after which they become (semi-) liquids, and on cooling again become solid. The melting or phase transition temperature depends on the polymer amount and/or composition of other additives present in the adhesive formulation. The temperature range typically varies from 60° C. to 250° C. depending on thermal properties, i.e. glass transition temperature of polymers and/or blends, of copolymers and additives used as coatings or for grafting purpose. Hot melt adhesives can commonly be derived from ethylene-vinyl acetate (EVA) copolymers, styrene-isoprene-styrene (SIS) copolymers, styrene-butadiene-styrene (SBS) copolymers, ethylene ethyl acrylate copolymers (EEA), and polyurethane reactive (PUR) generally with a polymer content ranging from 5% to 80%, and can have controllable water solubility. Examples of such adhesives can be found in U.S. Pat. No. 5,143,961 or U.S. Pat. No. 6,870,006. The “ring-and-ball” i.e. softening temperature of the hot melt adhesives typically ranges from 60° C. to 80° C.
U.S. Pat. No. 3,954,629 discloses the use of polyethylene, ethylene-vinyl acetate copolymer as a plugging agent in treating high-temperature, permeable oil-bearing formations.